Pulsed Electric Discharge Research Articles

Effect of High-Voltage Electrical Discharge Treatment of Diamond Powders on Their Mechanical Characteristics

The effect of pulsed high-voltage electrical discharge (HVED) treatment on the morphometrical, structural adsorption, and mechanical properties of diamond micropowders and abrasive powders is examined. These properties largely determine the performance and wear resistance of abrasive tools for machining process. It is shown that pulsed HVED treatment is efficient in the production of diamond micropowders and abrasive powders with low impurity content and high abrasive ability.

Theoretical and Experimental Research on Preparing Silicon Microspheres by Pulsed Electrical Discharge Method

In this paper, a new method of preparing silicon microspheres is introduced. Silicon microspheres have been produced under transient and high temperature generated with pulsed electrical discharge in the liquid. Their micro topography and composition are characterized and analyzed by SEM/EDS. The mechanism of sphere formation is studied by local area temperature field analysis using ANSYS. Various sizes of silicon particles (0.5-30μm) are successfully prepared under the different processing conditions. It is demonstrated that pulsed electrical discharge method is energy controllable, cost-effective, and is of great significance to the preparation of silicon ink which is the important material of new type of TFSC and selective emitter cell.

Micropatterning Polypyrrole Conducting Polymer by Pulsed Electrical Discharge

Polypyrrole and other conducting polymers are of interest in actuators, sensors, energy storage devices and organic electronics. The patterning of these polymers can be challenging, particularly polypyrrole due to its insolubility. This paper reports the first micropatterning of polypyrrole using high‐frequency pulses of extremely miniaturized electrical discharge. Microstructures with surface roughness of 70 nm are produced in the polymer with sub‐micron depth control. Patterning of polypyrrole film deposited on a commercial medical catheter is demonstrated toward enabling smart catheters that use the patterned film as integrated actuators. This novel micropatterning capability opens up new possibilities for polypyrrole and likely other polymers, promoting micro‐device applications for them.

Study of underwater shock waves and cavitation bubbles generated by pulsed electric discharges

The paper reports on generation of controllable underwater shock waves through the use of a magnetic pulsed compression circuit as the power source of underwater spark discharge to aid in improving accuracy and safety in medical applications. In the present work, we were able to widely change the peak pulsed voltages by the magnetic pulsed compression circuit. Sensitivity of underwater shock wave pressure to peak voltage variation was obtained near the electrodes in the 200 to 400 MPa range with voltage amplitudes from 10 to 18 kV. Effects of pulsed electric discharge parameters such as the voltage amplitude and pulse duration on characteristics of cavitation bubbles and shock waves were observed and analyzed. Visualization results and image analysis allowed evaluation of radii and collapse times of cavitation bubbles and their generated shock waves pressures. Pressures of underwater shock waves were also measured by a fiber optic probe hydrophone and were compared with the visualization analyses results.

Dynamics of shock waves appearing during pulsed high-current electric gas discharges. II. Regular polygonal shock waves with closed surface fronts

Dynamics of regular polygonal shock waves (SWs), generated at thin wire explosion, with a closed surface front and numbers of sides n = 3, 4, 5, 6, 8, 10, 12, and 16 in the plane of polygons is experimentally studied. Depending on the initial Mach number MPSW0 of such waves and the number n, two convergence modes are implemented: convergence with and without changes in the number of sides n. It is shown that the shape of the reflected wave front differs from the shape of the converging SW front for polygonal SWs with n ≥ 8, i.e., it becomes smooth. The number MPSW0 is determined depending on initial characteristics of an SW generator and gas. A significant amplification of such SWs with n ≥ 12 is observed near to the center of polygons; their maximum amplification is estimated.

Degradation of Synthetic Dyeing Wastewater by Underwater Electrical Discharge Processes

Electrical discharge treatments of synthetic dyeing wastewater were carried out with two different systems: underwater pulsed electrical discharge (UPED) and underwater dielectric barrier discharge (UDBD). Reactive Blue 4 (RB4) and Acid Red 4 (AR4) were used as model contaminants for the synthetic wastewater. The performance of the aforementioned systems was compared with respect to the chromaticity removal and the energy requirement. The results showed that the present electrical discharge systems were very effective for degradation of the dyes. The dependences of the dye degradation rate on treatment time, initial dye concentration, electrical energy, and the type of working gas including air, O2, and N2 were examined. The change in the initial dye concentration did not largely affect the degradation of either RB4 or AR4. The energy delivered to the UPED system was only partially utilized for generating reactive species capable of degrading the dyes, leading to higher energy requirement than the UDBD system. Among the working gases, the best performance was observed with O2. As the degradation proceeded, the concentration of total dissolved solids and the solution conductivity kept increasing while pH showed a decreasing trend, revealing that the dyes were effectively mineralized.

Oligopeptide Production from Alanine Monomer by Pulsed Corona Discharge Plasma in Ambient and Supercritical Argon

Supercritical carbon dioxide and electric discharge plasma could be one of reaction or extraction media for green chemical processes. Supercritical fluid is an attractive solvent due to its unique characteristic and transport physical properties. Taking advantage of these characteristics, this has been extensively investigated for extraction and chemical conversion technology. Although density of a supercritical fluid is high like a liquid, it is mobile like a gas because of low viscosity. On the other hand, the electron energy generated by electric discharge plasma in high pressure and a high-density domain generally serves as an index depending on the field intensity and medium density which were supplied to electric discharge space. From the above-mentioned viewpoint, the synergistic effect of combining electric pulsed plasma and supercritical fluids is expected as a new reaction process which may be able to enhance chemical reaction without using any catalysts. In this research, production of protein-like substance by pulse electric discharge plasma was carried out using amino acid in supercritical carbon dioxide. Moreover, nano pulse electric discharge plasma was also formed in supercritical fluids; reaction of amino acid was also observed. Aiming at establishment of a new reaction field, we did fusion research of supercritical fluids and electric discharge plasma. In this experiment, argon at the pressurized state was used as a reaction medium. Initially, alanine aqueous solution of 0.1 mol/L was loaded to a plasma reactor (inner volume: 600 mL) and reached under the desired conditions (290-308 K and 1-10.8 MPa). They were then analyzed by high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption time of flight mass spectroscopy (MALDI TOF-MS). The possibility of polymerization of alanine was realized from the compound after electric pulsed discharge plasma processing.

A study of mechanisms involved during the extraction of polyphenols from grape seeds by pulsed electrical discharges

Abstract This paper presents an experimental study of the influence of pulsed electrical discharges of low energy (3 to 10 J) on the extraction of polyphenols from grape seeds. To obtain a better understanding, three basic phenomena involved in the whole discharge process are studied separately: pulsed electric field (PEF), pre-breakdown phase (streamer), and breakdown phase (arc). The polyphenol extraction is much more efficient with arcs, compared to streamers and PEF. Therefore, during the discharge process, the enhancement of polyphenol extraction can be mainly ascribed to the final arc phase. The total energy per unit mass CWp required to extract 5000 mg GAE/100 g DM with the arc (CWp = 16 kJ/kg) is 27 times lower compared to streamers alone, and 47 times lower compared to PEF. An optical study shows that the mechanical effects of arcs (shock waves, expanding cavity, and strong turbulence) are much more pronounced compared to streamers. These mechanical effects are responsible for the fragmentation of grape seeds, and strongly promote the release of polyphenols. Other parameters such as the test cell shape and the inter-electrode distance also show that the polyphenol extraction is further enhanced when grape seeds are in close proximity with the breakdown arc. In optimized conditions, the extraction efficiency with low energy discharges can be significantly higher than previous measurements with high energy discharges. Industrial relevance This paper presents relevant information for the design of generating electrical discharges treatment. The study also addresses a specific case of use of by-products and shows the effectiveness of such technology.

Preparation of nonaggregated silver nanoparticles by the liquid phase plasma reduction method

Abstract

The Chlorella killed by pulsed electrical discharge in liquid with two different reactors

The application of pulsed high-voltage discharge in liquid has attracted wide attention as an effective water treatment. In this paper, two different liquid high-voltage discharge systems were constructed with plate-hole-plate and needle-plate electrode structures, and the inactivation behaviors of Chlorella were studied in the two reactors. The results show that the killing rates of algae in both reactors all increased significantly with increasing discharge voltage and the killing rates were intensely related to discharge power, instantaneous power and single pulse input energy. Furthermore, the inactivation effect in needle-plate reactor was superior to that in plate-hole-plate reactor under the same experimental conditions.

Modeling of Flyback Converter for Micro Machining Biomedical Component

Electrical Discharge Machining is a controlled process where pulsed electrical discharge is used to erode metal in a workpiece. A number of EDM power supplies utilizing different topologies have been widely developed for various applications. Nowadays, EDM process has been given a significant amount of research focus in manufacturing micro components with new low power topologies being utilized. Recently, a demand in micro machining has also extended into biomedical applications. In this paper a current mode flyback converter is implemented for micro machining biomedical component. A MATLAB/SIMULINK modeling technique of flyback converter is presented and the effectiveness of the flyback converter topology is evaluated through the simulation results obtained by varying the value of primary inductance

Pulsed Discharge Regeneration of Diesel Particulate Filters

A novel method for the removal of soot from a diesel particulate filter using pulsed electric discharges is presented. High voltage pulses of between 18 and 25 kV of nano to microsecond duration and with pulse energies of typically 100–200 mJ were applied to the filter via a series spark gap. Initial slow erosion of the soot layer proceeds via the formation of microdischarges. Subsequent spark discharges removed the accumulated soot more effectively from a larger filter volume. Average soot removal rates of ∼0.1–0.2 g/min were achieved at 50 Hz breakdown frequency by optimizing both electrode geometry and breakdown voltage. On-engine long term testing of the technology showed soot removal by pulsed discharge to be reliable, efficient and uniform; a total of 100 g of soot was deposited and removed over 18 filter regeneration cycles.

Formation of Nitrite- and Nitrate-Ions in Aqueous Solutions Treated with Pulsed Electric Discharges

The accumulation of nitrogen-containing ions formed in aqueous solutions dispersed in air and treated with pulsed corona, dielectric barrier and spark electric discharges, was studied dependent on electric conductivity and pH of treated solutions. The impact of conductivity to the spark and corona discharge is determined by the increased ohmic losses in the reactor. In contrast, the character of dielectric barrier discharge is significantly changed with growing conductivity resulted in increased nitrite-to-nitrate ratio. In alkaline solutions the production of nitrites is increased for the spark and the barrier discharge; the corona discharge produce only nitrates. The amount of nitrates produced in pulsed corona discharge at energy doses characteristic for potable water treatment is about 100 times lower than their maximum permissible concentration.

Time-resolved characterization of a pulsed discharge in a stationary bubble

In recent years, plasma generation in water has been proposed for the application of water treatment. The process efficiency is believed to be improved by the introduction of bubbles in the plasma active region. For further optimization, the initiating and developmental mechanisms of plasma inside bubbles need to be understood to a greater extent. In order to meet this necessity, we investigated pulsed electrical discharge inside a stationary bubble in water. This paper deals with the evolution of the discharge and of the bubble shape during discharge, investigated by electrical characterization and fast imaging. Only several microseconds after the application of the voltage pulse, plasma light is observed. Different phases are observed during plasma formation. The plasma is strongest at the bubble surface, causing the surrounding water to evaporate. This leads to both the formation of propagating streamers into the water and the expansion and collapse of the bubble. These observations show that plasma inside a bubble has the strongest activity at the bubble surface, making it attractive for water treatment.

Dynamics of bubble generated by low energy pulsed electric discharge in water

Results of investigations of bubble formation and dynamics for discharge in water are presented. Experiments were carried out in discharge chamber with axisymmetric electrode system “wire to wire”. Interelectrode gap was varied from 1 to 10 mm. Energy in a pulse was <1 J. Velocity of bubble expantion and collapse is about several hundreds meter per second at early stage of discharge. Bubble pulsation period is 0.5 – 1 ms. Increasing of energy released in the discharge gap will increase bubble pulsation period. Little bubble was formed by reducing energy input into discharge. But the main stage of discharge always followed by bubble formation. Specific erosion is measured for different energy in pulse and matched up with bubble collapse.

Shock waves in water at low energy pulsed electric discharges

Experimental results of shock wave formation and propagation in water at low energy pulsed electric discharges are presented. To study the hydrodynamic structure of the shock waves, the direct shadow optical diagnostic device with time resolution of 5 ns and spatial resolution of 0.1 mm was designed and developed. Synchronization of the diagnostic and electrodischarge units by the fast optocouplers was carried out. The dependences of shock wave velocities after breakdown of interelectrode gap for various energy inputs (at range of ≤1 J) into discharge were obtained. Based on the experimental results the recommendations for the adjustment parameters of the power supply and load were suggested.

Analysis of physicochemical properties of nanoparticles obtained by pulsed electric discharges in water

Aqueous dispersions of nanoparticles are obtained by pulsed electric discharges in water between silver, copper, and iron electrodes. It is shown that depending on the type of the electrode metal, metallic and oxide nanoparticles with the I and II degrees of oxidation, as well as nanoparticles with the magnetite and hematite structure, are formed.

Pulsed electric discharges in water as a source of magnetic nanoparticles for transportation of microorganisms

The distinguishing property of magnetic nanoparticles that determines the increasing interest in these objects is their mobility under the action of a magnetic field, which can be used for their directional transportation, deposition, and concentration in a preset region. It is shown that nanoparticles consisting of iron oxide can be used as magnetoactive agents for converting the cells of microorganisms into microaggregates for their directional transportation or concentration in liquid media under the action of a magnetic field.

Oxidation of iron (II) in sulfuric acid solutions by a pulsed electric discharge

Physical features of application of pulsed electric discharges in a two-phase gas-liquid medium for activation of ferrous iron oxidation processes in sulfuric acid technological solutions are considered. The main parameters influencing the iron oxidation efficiency are determined.

Time-Resolved High-Speed Visualization and Analysis of Underwater Shock Wave Focusing Generated by a Magnetic Pulse Compression Unit

Paper reports on visualization and analysis of underwater shock waves generation, focusing, and propagation. Recently, shock waves have been attractive with rising attention in medical field. Extracorporeal shock wave lithotripter has been one of its very successful applications. However, the effects of shock waves on living tissue are not sufficiently understood, due to unknown parameters involving the shock wave interaction. For better understanding of affecting points, a precise and controllable shock wave source is required. In this paper, in order to study shock wave effects, pulsed electric discharges produced by magnetic pulse compression circuit were used to generate underwater shock waves. A half-ellipsoidal reflector was used for shock wave focusing. The whole sequences of the shock wave generation, propagation, focusing, and cavitation bubbles, which appeared after shock wave passage, were visualized by time-resolved high-speed shadowgraph method. The peak pressure of shock wave focusing at second focal point reached 180 MPa. A cylindrical test section was used to observe phenomena around the electrode from the pulse discharge to bubble collapse. The first cavitation bubble's collapse occurred at about 750 μs. In the experiment, the two shock waves, one generated by expansion of plasma and another generated by collapse of the cavitation bubble were studied. Using high-speed visualization and image analysis, the velocity and pressure of the two shock waves were evaluated. The peak pressure of shock wave generated by bubble collapse reached 157 MPa.